Various methods of producing activated carbon are known. Generally, these methods seek to form the largest possible number of capillary cavities or pores transforming the carbon into smaller particles. It is desired to obtain as large a combined interior surface as possible which in turn is formed by the surfaces of the individual carbon particles or crystallites which form the desired absorption medium. The formation of the large number of pores supported by the surrounding carbon structure is normally accomplished through the controlled thermal decomposition of organic substances.
Absorption techniques require activated carbon with the highest possible activation which in turn had led to the development of a variety of activation methods.
The simple low temperature carbonization, e.g., smoldering, has become insufficient for this purpose. Smoldering does form surface enlargening pores or cavities; however, it simultaneously entails a shrinking of the remaining carbon structure. To achieve a further surface enlargement, gas activation methods have been developed which achieve the selective oxidation of the base carbon with oxidizing agents including steam, carbon dioxide or oxygen shedding gasses for developing the pore or cavity structure.
Chemical activation methods have also been developed which can use carbonizable raw materials. The object of the chemical activation is to at least maintain the relatively large distances between the carbon atoms as are found in organic raw materials. This is accomplished through the removal of non-carbon elements which usually includes the dehydration of the material. The use of zinc chloride for soaking the raw material is well known. The material is thereafter thermally treated.
There are also methods for chemically activating carbon in which the medium is not preferentially dehydrated. The impregnation of the base material with such compounds as potassium sulfite or potassium thiocyanate also causes the maintenance of the original carbon structure during the thermal treatment of the mash and the water removal therefrom. The chemical substance remaining after the carbonization causes a further corrosion of the carbon substance, through oxidation for example to thereby enlarge the respective distances of the carbon atoms as in the gas activation process.
The above discussed known methods have the drawback that the required apparatus must be specifically constructed for the respective processes. In other words, in accordance with the prior art two or more of the described carbon activation processes cannot be practiced in one and the same installation, particularly if a high degree of automation is desired.
Another shortcoming of the known carbon activation method is that the gasses that are liberated during the thermal decomposition as well as the heat that is necessary for the thermal composition cannot and/or are not utilized so that economic losses are incurred.